How to eliminate/reduce noise in volume renders?

[magneto]

Hi,

 

When I render a volume, there seem to be a lot of noise present. I changed Min/Max Ray Samples to 32, reduced Noise Level to 0.001, increased Volume Quality to 5 and Volume Shadow Quality to 3 but still has lots of noise.

 

Is this normal for volumes? Does it have to do with the shader (Basic Smoke)?

 

 

 

Thanks

[jkunz07]

I think the first thing to do when reducing noise in volume renders is to start increasing transparent samples / stochiastic transparency

[magneto]

Thanks jkunz that reduced the noise significantly. Is there a general value to aim for or is it just by judging from the render to render? It's hard to assess how much time it adds to renders, but it's not linear. I set it to 64 and it's hard to notice any noise.

[Annon]

64 is very high. Usually 2-4 should decrese a lot of noise. Also the ray bias (set to 0.05 by default) down a bit will smooth off the noise as well.

[Annon]

Also turn off sample lock so your noise doesn't stick, giving you a more grain look rather than render noise.

[old school]

Transparent Samples is the first thing to adjust when you find you are getting the "salt and pepper" look in your volume. The default of 4 is a starting point that may work for dense volumes but less so for transparent volumes.

 

If you have objects with an opacity that is not 0 or 1 with Stochastic Transparency enabled, you will be firing opacity rays first. Houdini does this prior to firing shading rays. It computes the transparency by partitioning the surface shader and evaluating only the part of the shader that computes final opacity or Of. This is what makes this very efficient. You have decoupled the opacity rays from the sample rays. This also means if you are creating your own shaders, keep the Of opacity path clear of any shading models.

 

If you have Stochastic Transparency off, each ray will compute opacity first and then colour. Not as efficient.

[magneto]

Thanks alot guys. The default was 4 and already looked like the pic in the OP.

 

Also where is the Ray Bias parameter? I couldn't find it. Is it a hidden Rendering parameter I should add using the Edit Parameter Interface?

 

I wasn't sure what value was sufficient, that's why I set it to 64 after 16 which still had a lot of noise. I just wanted to see how much clear I can get without increasing way too much. The increased render time from 16 to 64 didn't seem anything I could notice though.